There are a variety of types of analog-to-digital (AD) converters including a flash converter, a successive-approximation converter, a pipeline converter, a cyclic converter, and a ΔΣ modulator converter. In particular, the cyclic converter and the ΔΣ modulator converter are capable of improving conversion accuracy by increasing the number of conversion cycles, and therefore can be regarded as an incremental AD converter.
In an actual design, in the case of a circuit configuration of the cyclic converter, the accuracy of an analog element (especially amplifier element) limits the accuracy of the whole system, so that there is a limit to the improvement in the accuracy. On the other hand, in the case of a circuit configuration of the ΔΣ modulator converter, the conversion accuracy can be improved by simply increasing only the number of conversion cycles instead of improving the accuracy of an analog element that is used. As described above, Non Patent Literature (NPL) 1 discloses that the circuit configuration of the ΔΣ modulator converter is suitable specifically for the incremental AD converter. NPL 1 also discloses that the accuracy can be improved by combining a 2nd- or higher-order ΔΣ modulator AD converter and a decimation filter which calculates an output pulse train.